The steroid hormones (estrogen and progesterone) stimulate growth, maturation and the development of new biochemical capacities in their reproductive target organs. These steroids play a major role in maternal physiology and fetal development and their relationships to reproductive tissue malignancy are well established. Although steroid hormones exert major influences on nucleic acid and protein metabolism, the exact biochemical processes by which sex hormones regulate growth and function in target tissues are not yet clear. The general objectives of these studies are to define the mechanism of action of reproductive hormones in regulating cell replication, morphologic differentiation and biochemical specialization in their target tissues. This will be accomplished by coordinating a network of separate in vivo and in vitro investigations in a single experimental animal model system in which specific biochemical events can be studied easily -- the chick oviduct. These studies will involve aspects of cell physiology, structural anatomy, nucleic acid and protein chemistry, immunology, and related intermediary metabolism; emphasis will rest heavily on regulation of nucleic acid and protein synthesis. It is expected that the understanding derived from this project will be relevant to the biology of the natural reproductive hormones relative to maternal physiology and fetal development. The following proposed studies should also be pertinent to development of more precise theories for the biochemical mechanism of action of hormones in general and more specifically steroid sex hormones.